Heat oven to 350º.
In a mixer, cream the butter and sugar until fluffy.
Add yolks and vanilla.
Stir in the dry ingredients.
Press the dough into the bottom and sides of a 9 inch tart pan with removable bottom.
Chill 30 minutes.
Prick bottom with fork and bake 20 minutes.
Cool.
While tart bakes, heat walnuts in a dry frying pan over med/low heat. Cook until fragrant and toasted. Let cool. Sprinkle over the cookie crust.